Method of servicing a wellbore with a sealant composition comprising solid latex

ABSTRACT

A method of servicing a wellbore comprising placing a sealant composition comprising solid latex into the wellbore.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to commonly owned U.S. patent applicationSer. No. 10/______, [Attorney Docket No. 2005-IP-017357U1] entitled“Sealant Compositions Comprising Solid Latex,” filed on the same date asthe present application and incorporated by reference herein.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to servicing a wellbore. More specifically, itrelates to the use of solid latex in wellbore servicing fluids.

2. Background of the Invention

Natural resources such as gas, oil, and water residing in a subterraneanformation or zone are usually recovered by drilling a wellbore down tothe subterranean formation while circulating a drilling fluid in thewellbore. After terminating the circulation of the drilling fluid, astring of pipe, e.g., casing, is run in the wellbore. The drilling fluidis then usually circulated downward through the interior of the pipe andupward through the annulus, which is located between the exterior of thepipe and the walls of the wellbore. Next, primary cementing is typicallyperformed whereby a cement slurry is placed in the annulus and permittedto set into a hard mass (i.e., sheath) to thereby attach the string ofpipe to the walls of the wellbore and seal the annulus. Subsequentsecondary cementing operations may also be performed.

Fluids used in servicing a wellbore may be lost to the subterraneanformation while circulating the fluids in the wellbore. These fluids mayenter the subterranean formation via various types of leak-off flowpaths in permeable zones such as depleted zones, zones of relatively lowpressure, lost circulation zones having naturally occurring fractures,weak zones having fracture gradients exceeded by the hydrostaticpressure of the servicing fluid, and so forth. As a result, the serviceprovided by such fluids is more difficult to achieve. Also, the loss ofsuch fluids increases the cost of the overall operation due to theprolonged rig time required, the fluids being relatively expensive, andpossibly a need to install additional casing.

There are a variety of methodologies for combating drilling fluidcirculation losses. Such methodologies may involve adding lossprevention materials to the drilling fluid itself and continue thedrilling process or pump fluid until fluid circulation is restored ormay involve the use of a two-stream process. In a two-stream process,two fluid streams are introduced to the loss circulation area, forexample by pumping one stream down the drillstring and one stream downthe annulus, or alternatively via sequential pumping down thedrillstring, annulus or both. These streams when mixed downhole near theloss circulation zones combine to rapidly form a viscous mass, which isdesigned to prevent further loss of drilling fluid into the fractures.

When such methods are successful in mitigating drilling fluidcirculation losses, the operators have two options for follow-upoperations. Their first option is to temporarily stop the drillingoperation, case the well bore and cement the casing before resumingfurther drilling. This may result in a reduced well bore diameter fromthat point forward resulting in a smaller than planned pipe across theproduction intervals. During production, these reduced production pipestring diameters induce high friction pressures that restrict or limitproduction rates and negatively effect well production economics. Thispractice is adapted when the loss circulation sealant is not strongenough to withstand hydrostatic pressure of the drilling fluid ifdrilling is resumed without casing the well bore. The second option ismore economical during the well construction phase and more profitableduring the production phase. The second option involves using a losscirculation sealant that provides sufficient strength and reinforcementto the loss circulation zone so that it can withstand hydrostaticpressure from further drilling without resorting to casing the wellbore.This strengthening process is often referred to as increasing theWellbore Pressure Containment Integrity (WPCI). This will not only savethe cost of installing the extra casing or liner pipe strings, but itwill also allow well completion with the planned well bore diameter thatis required to achieve the expected production rates. In some cases, itwill also lead to a wider than planned well bore diameter which afterwell completion and suitable stimulation operations, may facilitateincreased production rates. The second option is a process referred toas a “Drill Ahead” process in the industry and in the later sections ofthis application. A “Drill Ahead” process and associated methods forintroducing WPCI compositions into a wellbore to seal subterranean zonesare described in U.S. Pat. No. 6,926,081B2, and in U.S. patentapplication Ser. No. 10/350,429 entitled “Methods of Improving Well BorePressure Containment Integrity” and filed on Jan. 24, 2003, which areincorporated by reference herein in their entirety.

Sealant compositions for use in fluid circulation losses may containmodifiers to enhance the mechanical properties of the sealant. Latexemulsions, which may contain a stable water-insoluble, polymericcolloidal suspension in an aqueous solution, are commonly used insealant compositions to improve the properties of those compositions.For example, latex emulsions are used in cement compositions to reducethe loss of fluid there from and to reduce the cement's permeability togas thereby substantially increasing the cement's resistance to gas flowfrom a gas-bearing formation. Latex emulsions are also employed toreduce the brittleness and improve the flexibility of sealantcompositions; otherwise, the compositions may shatter under the impactsand shocks generated by drilling and other well operations. For example,with regard to fluid circulation loss, a two-stream process has beenused where the first stream may be the drilling fluid itself or adesigned fluid containing key ingredients while the second stream maycomprise a latex emulsion. This process has found good commercialsuccess in combating drilling fluid circulation losses especially in thecase of oil-based muds (OBM).

The use of latex emulsions for combating drilling fluid circulationlosses has some disadvantages. In the case of the two stream processes,preparing the latex-containing stream is operationally cumbersome andrequires mixing an aqueous latex fluid, an aqueous stabilizing liquidsurfactant and a dry solids blend prior to placing in a wellbore. Thisoperation requires storage of two fluid components and a dry solidcomponent. Also, there can be a substantial costs incurred for theshipping, storing and handling of latex emulsions. Furthermore, latexemulsions and the aqueous stabilizing surfactants present potentialspill and leak related health, safety and environment (HSE) hazards.Frequently, it is operationally preferred and more cost effective todesign cement slurries that use all solid components so that a singledry blend can be made in a bulk blending facility and transported to thefield location where it is mixed with water prior to pumping. Use ofaqueous latex emulsion requires more complex mixing operations.

Given the foregoing problems it would be desirable to develop a methodof reducing the costs and HSE hazards associated with the use of latexin sealant compositions. Furthermore, it would be desirable to develop amethod of preparing sealant compositions with latex that isoperationally facile.

BRIEF SUMMARY OF SOME OF THE PREFERRED EMBODIMENTS

Disclosed herein is a method of servicing a wellbore comprising placinga sealant composition comprising solid latex into the wellbore.

The foregoing has outlined rather broadly the features and technicaladvantages of the present invention in order that the detaileddescription of the invention that follows may be better understood.Additional features and advantages of the invention will be describedhereinafter that form the subject of the claims of the invention. Itshould be appreciated by those skilled in the art that the conceptionand the specific embodiments disclosed may be readily utilized as abasis for modifying or designing other structures for carrying out thesame purposes of the present invention. It should also be realized bythose skilled in the art that such equivalent constructions do notdepart from the spirit and scope of the invention as set forth in theappended claims.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Disclosed herein are sealant compositions comprising a solid latex. Suchcompositions may additionally comprise cement. Such compositions mayadditionally comprise an organophilic clay, one or more viscosifiers, orcombinations thereof. In various embodiments, the sealant compositioncomprises a solid latex and cement; alternatively, a solid latex,cement, and an organophilic clay; alternatively, a solid latex, cement,and one or more viscosifiers; alternatively a solid latex, cement, anorganophilic clay and one or more viscosifiers; alternatively solidlatex and organophilic clay; alternatively solid latex and one or moreviscosifiers; or alternatively a solid latex, organophilic clay, and oneor more viscosifiers. In various embodiments, the sealant compositioncomprising a solid latex may be contacted with one or more other fluidsprior to, during, after, or concurrently with being placed down hole,for example contact with an oil based mud (OBM), a water based mud(WBM), an aqueous fluid containing a pH increasing material, or acombination thereof.

The sealant composition can be used for any purpose, for example as losscirculation fluids, fracture sealants, zonal isolation fluids, andcementing fluids. In an embodiment, the sealant composition may be usedto service a wellbore that penetrates a subterranean formation. It is tobe understood that “subterranean formation” encompasses both areas belowexposed earth and areas below earth covered by water such as ocean orfresh water. Without limitation, servicing the wellbore includespositioning the sealant composition in the wellbore to isolate thesubterranean formation from a portion of the wellbore; to support aconduit in the wellbore; to plug a void or crack in the conduit; to pluga void or crack in a cement sheath disposed in an annulus of thewellbore; to plug an opening between the cement sheath and the conduit;to prevent the loss of aqueous or non-aqueous drilling fluids into losscirculation zones such as a void, vugular zone, or fracture; to be usedas a fluid in front of cement slurry in cementing operations; to seal anannulus between the wellbore and an expandable pipe or pipe string; orcombinations thereof.

In an embodiment, the sealant composition comprises a solid latex, areconstituted solid latex or combinations thereof. Herein a “solidlatex” refers to latex which is a free flowing particulate material thatis substantially dry or free of fluid. Solid latexes may be prepared byremoving water from any emulsion polymerized polymer systems such asthose to be described herein. Methods of removing the water fromemulsion polymerized polymer systems are known to one of ordinary skillin the art and include without limitation techniques such as spraydrying. Herein a “reconstituted solid latex” refers to a latex solutionor emulsion, typically a stable emulsion, that is prepared from a solidlatex. Herein “reconstituting” refers to the process of resuspending orsolvating a solid latex in a suitable fluid. Aqueous fluids such asfresh or salt water and/or nonaqueous fluids such as diesel, kerosene,mineral oil, esters, linear and poly alpha-olefins, or combinationsthereof may be used to resuspend the solid latex and form a stable latexemulsion. A reconstituted solid latex is formed from dry latexparticles, which is in contrast to a liquid latex emulsion that isformed by emulsion polymerization in which the polymer particles haveremained in a liquefied state and have not undergone a dry, particulatestate.

An emulsion polymerized latex system may comprise monomers that includepolar monomers and non-polar monomers such as ethylenically unsaturatedcarboxylic acids (e.g., acrylic acid), vinyl nitrile (e,.g.,acrylonitrile), aromatic and aliphatic olefins and dienes, orcombinations thereof. For example, the solid latex may comprise latexformed from monomers that include, without limitation, vinyl aromaticmonomers (e.g., styrene based monomers), ethylene, butadiene,vinylnitrile (e.g., acrylonitrile), olefinically unsaturated esters ofC₁-C₈ alcohol, ethylenically unsaturated carboxylic acids, orcombinations thereof. In some embodiments, non-ionic monomers thatexhibit steric effects and that contain long ethoxylate or hydrocarbontails may also be present. Other suitable types of solid latexes may beprepared from colloidally stabilized or alkali swellable latexes asdisclosed herein. Suitable emulsifying surfactants may be includedduring the polymerization phase to obtain a stable emulsion. An exampleof a solid latex includes without limitation RHOXIMAT PSB 150 latexpowder which is a styrene butadiene copolymer resin in powder formcommercially available from Rhodia Corporation, Cranbury, N.J.

In an embodiment, the solid latex is prepared from a colloidallystabilized latex emulsion. As used herein, “colloidally stabilized latexemulsion” refers to a latex comprising polymer particles suspended in anaqueous solution and at least one protective colloid for providingstabilization to the colloidal polymer emulsion. Protective colloidsknown in the art may be employed in the colloidally stabilized latexemulsion. Examples of suitable protective colloids include, but are notlimited to, partially and fully hydrolyzed polyvinyl alcohols, celluloseethers such as hydroxymethyl cellulose, hydroxyethyl cellulose,hydroxypropyl cellulose, starch and starch derivatives, andcarboxymethyl cellulose, natural and synthetic gums such as gumtragacanth and gum arabic, polyacrylic acid, acrylates, poly(vinylalcohol)co(vinyl amine) copolymers, and combinations thereof.

In an embodiment, the polymer contained in the colloidally stabilizedlatex emulsion may comprise an aliphatic conjugated diene monomer and atleast one additional monomer comprising a non-aromatic unsaturated mono-or di-carboxylic ester monomer, an aromatic unsaturated monomer, atleast one nitrogen-containing monomer, or combinations thereof. Examplesof suitable aliphatic conjugated diene monomers include, but are notlimited to, C₄ to C₉ dienes such as butadiene monomers, e.g.,1,3-butadiene, 2-methyl-1,3-butadiene, 2 chloro-1,3 butadiene,2-methyl-1,3-butadiene, and 2 chloro-1,3-butadiene. Blends or copolymersof the diene monomers may also be used. Examples of suitablenon-aromatic unsaturated monocarboxylic ester monomers include, but arenot limited to, acrylates, methacrylates, and combinations thereof. Theacrylates and methacrylates may include functional groups such as aminogroups, hydroxy groups, and epoxy groups. Examples of suitablenon-aromatic unsaturated dicarboxylic ester monomers include, but arenot limited to, alkyl and dialkyl fumarates, itaconates, maleates, andcombinations thereof, with the alkyl group having from one to eightcarbons. In an embodiment, a non-aromatic unsaturated monocarboxylicester monomer employed in the colloidally stabilized latex is methylmethacrylate. Examples of suitable aromatic unsaturated monomersinclude, but are not limited to, styrene and styrene derivatives such asalphamethylstyrene, p-methyl styrene, divinyl benzene, vinyltolunene,divinyl toluene, ethylstyrene, tert-butyl styrene, monochlorostyrene,dichlorostyrene, vinyl benzyl chloride, fluorostyrene, alkoxystyrenes(e.g., paramethoxystyrene), and combinations thereof. In an embodiment,an aromatic unsaturated monomer included in the colloidally stabilizedlatex is styrene. Examples of suitable nitrogen-containing monomersinclude, but are not limited to, acrylonitrile, methacrylonitrile,acrylamide, methacrylamide, N-methylolacrylamide, alkylatedN-methylolacrylamides such as N-methoxymethylacrylamide andN-butoxymethylacrylamide, acrolein, and combinations thereof. In anembodiment, a nitrogen-containing monomer included in the colloidallystabilized latex is acrylonitrile.

In one embodiment, the colloidally stabilized latex also includes asurfactant having ethylenic unsaturation, an oxyalkylene functionalmonomer, or combinations thereof incorporated in the backbone of thepolymer. The surfactant is copolymerized with the aliphatic conjugateddiene monomer and the additional monomer and may be located at thesurface of the polymer particles. Since the surfactant is an integralpart of the polymer, it most likely cannot desorb from the polymer.Examples of suitable surfactants are disclosed in U.S. Pat. No.5,296,627, which is incorporated by reference herein in its entirety.The surfactant may have a hydrophobic portion that possesses terminalethylenic unsaturation and a hydrophilic portion that contains apoly(alkyleneoxy) segment. Examples of suitable oxyalkylene functionalmonomers include, but are not limited to, monoesters of carboxylic acidor dicarboxylic acid, diesters of dicarboxylic acid, compounds generallyrepresented by the following formulas, and combinations thereof:

where R is hydrogen or a C₁-C₄ alkyl, R′ is hydrogen or a C₁-C₄ alkyl,R″ is hydrogen or a C₁-C₄ alkyl, and n is in a range of from 1 to 30.The oxyalkylene functional monomer is copolymerized with the aliphaticconjugated diene monomer and the additional monomer. Additional examplesof surfactants and oxyalkylene functional monomers that may be employedin the colloidally stabilized latex are provided in aforementioned U.S.Pat. No. 5,900,451 which is incorporated by reference herein in itsentirety.

In the foregoing embodiment in which the colloidally stabilized latexincludes a surfactant having ethylenic unsaturation and/or anoxyalkylene functional monomer, the amount of protective colloid presentin the colloidally stabilized latex is in the range of from about 0.1percent (hereinafter “%”) to about 10% by total weight of the startingmonomers, alternatively from about 1% to about 8%, alternatively fromabout 2% to about 6%. The amount of aliphatic conjugated diene monomerpresent in the colloidally stabilized latex is in the range of fromabout 5% to about 95% by total weight of the starting monomers,alternatively from about 20% to about 80%. The amount of non-aromaticunsaturated mono- or di-carboxylic ester monomer present in thecolloidally stabilized latex is in the range of from about 5% to about95% by total weight of the starting monomers, alternatively from about20% to about 80%. The amount of aromatic unsaturated monomer present inthe colloidally stabilized latex is in the range of from about 5% toabout 95% by total weight of the starting monomers, alternatively fromabout 20% to about 80%. The amount of nitrogen-containing monomerpresent in the colloidally stabilized latex is in the range of fromabout 5% to about 95% by total weight of the starting monomers,alternatively from about 20% to about 80%. The amount of surfactantpresent in the colloidally stabilized latex is in the range of fromabout 0.1% to about 5% by total weight of the starting monomers,alternatively from about 1% to about 4%, alternatively from about 2% toabout 3%. The amount of oxyalkylene functional monomer present in thecolloidally stabilized latex is in the range of from about 0.1% to about7% by total weight of the starting monomers, alternatively from about 1%to about 3%. When the surfactant and the oxyalkylene functional monomerare both used, the colloidally stabilized latex may contain from about0.5% to about 2% of the surfactant and from about 1% to about 3% of theoxyalkylene functional monomer by total weight of the starting monomers.

In another embodiment, the colloidally stabilized latex includes afunctionalized silane incorporated in the polymer that is capable ofadsorbing the protective colloid. Examples of suitable functionalizedsilanes are generally represented by the following formula:

where R″ is a C₁ to C₅ alkyl, R′ is a C₁ to C₅ alkyl, R is SH, CH₂═CH—,CH₂═C(CH₃)—C(O)O—, CH₂═CH—C(O)O—, and

n is in a range of from 1 to 10, and m is 2 or 3. An example of asuitable functionalized silane includes without limitation, gammamercaptopropyl trimethoxy silane in which R is SH, R′ is C₁ alkyl, n is3, and m is 3. Unsaturated mono- or di-carboxylic acid monomers andderivatives thereof, such as acrylic acid, methacrylic acid, itaconicacid, fumaric acid, and malieic acid, may also be employed in thecolloidally stabilized latex. Additional examples of surfactants andoxyalkylnlene functional monomers that may be employed in thecolloidally stabilized latex are provided in U.S. Pat. No. 6,130,287,which is incorporated by reference herein in its entirety.

In the foregoing embodiment in which the colloidally stabilized latexincludes a functionalized silane, the amount of protective colloidpresent in the latex is in the range of from about 1 percent(hereinafter “%”) to about 10% by total weight of the starting monomers.The amount of aliphatic conjugated diene monomer present in thecolloidally stabilized latex is in the range of from about 1% to about99% by total weight of the starting monomers, alternatively from about10% to about 70%, alternatively from about 20% to about 50%. The amountof non-aromatic unsaturated mono- or di-carboxylic ester monomer presentin the colloidally stabilized latex is in the range of from about 1% toabout 99% by total weight of the starting monomers, altemtaively fromabout 50% to about 80%. The flinctionalized silane may be present in thecolloidally stabilized latex in various amounts. For example, the amountof silane present in the polymer may range from about 0.01% to about 2%by total weight of the starting monomers, alternatively about 0.5%.

Examples of suitable colloidally stabilized latexes for use in thesealant compositions and methods of making such latexes are described inU.S. Pat. Nos. 5,900,451 and 6,130,287, referenced previously. In thosepatents, the colloidally stabilized latexes are referred to as“stabilized emulsion polymers.” An example of a suitable latex includeswithout limitation a carboxylated butadiene acrylonitrile latex sold asBS2100 by Dow Reichhold Inc.

In an embodiment, the solid latex is prepared from an alkali swellablelatex. “Alkali swellable latex” is defined as a latex material that,when exposed to pH increasing materials, may swell and exhibit anincrease in viscosity. Such pH increasing materials may be added to thelatex emulsion prior to pumping or may be caused to mix with the latexdown hole, for example in a two-stream pumping method. Examples of pHincreasing materials include without limitation alkali, alkaline earth,and transition metal hydroxides, carbonates, bicarbonates, phosphates,organic amines and the like in encapsulated or unencapsulated form. Inan embodiment, a sealant composition comprises an alkali swellable solidlatex and a pH increasing material.

Alkali swellable latexes typically contain, in addition to the typicallatex forming monomers, monomers having acidic groups capable ofreacting with the pH increasing materials thereby forming anionicpendant groups on the polymer backbone. Alkali swellable latexemulsions, due to the presence of acidic groups, have a pH in the rangeof from about 2 to about 8 and are predominantly low viscosity fluidswith viscosities less than about 100 centipoise for an emulsioncontaining about 30% to 50% solids. When the pH is increased by theaddition of a pH increasing material, the viscosity increase may be inthe range of from about five times to more than about a million timesfor a 30% emulsion. The conventional latex emulsion does notsignificantly increase in viscosity upon the addition of a pH increasingmaterial. In some embodiments, the latex emulsion may be partiallycross-linked during the polymerization phase of the monomers. Examplesof typical latex forming monomers that may be used to make alkaliswellable latexes include, without limitation, vinyl aromatic monomers(e.g., styrene based monomers), ethylene, butadiene, vinylnitrile (e.g.,acrylonitrile), olefinically unsaturated esters of C₁-C₈ alcohol, orcombinations thereof. In some embodiments, non-ionic monomers thatexhibit steric effects and that contain long ethoxylate or hydrocarbontails may also be present. The monomers containing acid groups capableof reacting with pH increasing materials include ethylenicallyunsaturated monomers containing at least one carboxylic acid functionalgroup. Such carboxylic acid containing monomers may be present in therange of from about 5% to about 30% by weight of the total monomercomposition used in preparing the alkali swellable latex. Withoutlimitation, examples of such carboxylic acid containing groups includeacrylic acid, alkyl acrylic acids, such as methacrylic acid andethacrylic acid, alpha-chloro-acrylic acid, alpha-cyano acrylic acid,alpha-chloro-methacrylic acid, alpha-cyano methacrylic acid, crotonicacid, alpha-phenyl acrylic acid, beta-acryloxy propionic acid, sorbicacid, alpha-chloro sorbic acid, angelic acid, cinnamic acid, p-chlorocinnamic acid, beta-styryl acrylic acid (1-carboxy-4-phenylbutadiene-1,3), itaconic acid, maleic acid, citraconic acid, mesaconicacid, glutaconic acid, aconitic acid, fumaric acid, tricarboxy ethylene,or combinations thereof. In an embodiment, the carboxylic acidcontaining groups can include itaconic acid, acrylic acid, orcombinations thereof.

The preparation of such alkali swellable latexes is discussed in U.S.Pat. Nos. 3,793,244; 4,861,822; and 5,563,201, which are incorporatedherein by reference in their entirety. An example of a commerciallyavailable alkali swellable dry solid latex includes without limitationTYCHEM CPS 986 available from Dow Reichhold, Research Triangle, NorthCarolina.

In an embodiment, the latex materials disclosed herein are originally inan emulsified form, e.g., a colloidally stabilized latex, and areconverted to a solid form through the removal of water as previouslydescribed. In another embodiment, a solid latex is reconstituted into alatex emulsion through the addition of water. The latex materials, as asolid, a reconstituted emulsion, or combinations thereof, may beincorporated into the sealant compositions to improve the physical andmechanical properties thereof. The relative amounts of the latex in aparticular sealant composition depend upon the intended use of theresulting composition. For example, a cementitious sealant compositionmay contain from about 0.1% to about 25% solid latex by weight of cement(bwoc), alternatively from about 0.5% to about 20% solid latex bwoc,alternatively from about 1% to about 20% solid latex bwoc, alternativelyfrom about 1% to about 15% solid latex bwoc, alternatively from about 1%to about 10% solid latex bwoc. In compositions without cement, theamount of solid latex may be in the range of 5% to 50% by weight of thetotal composition, alternatively, 10% to 35% by weight of the totalcomposition, alternatively 15% to 25% by weight of the totalcomposition.

In an embodiment, the sealant composition comprises a cement. Thesealant composition may comprise a cement such as hydraulic cement,which includes calcium, aluminum, silicon, oxygen, and/or sulfur andwhich sets and hardens by reaction with water. Examples of hydrauliccements include but are not limited to Portland cements (e.g., classesA, C, G, and H Portland cements), pozzolana cements, gypsum cements,phosphate cements, high alumina content cements, silica cements, highalkalinity cements, and combinations thereof.

In an embodiment, the sealant composition includes a sufficient amountof water to form a pumpable cementitious slurry. The water may be freshwater or salt water, e.g., an unsaturated aqueous salt solution or asaturated aqueous salt solution such as brine or seawater. The water maybe present in the amount from about 20 to about 180 percent by weight ofcement, alternatively from about 28 to about 60 percent by weight ofcement. The cement compositions may comprise a density from about 4lb/gallon to about 23 lb/gallon. In alternative embodiments, the cementcompositions may comprise a density from about 12 lb/gallon to about 17lb/gallon. In other alternative embodiments, the cement compositions maybe low-density cement compositions with a density from about 6 lb/gallonto about 14 lb/gallon.

In an embodiment, the sealant composition comprises an organophilicclay. Without wishing to be limited by theory, the organophilic clay mayinteract by absorption with any oil present in the non-aqueous oil-baseddrilling fluid, in the formation (for example in the lost circulationzone), or pumped as a two-stream component. The interaction of theorganophillic clay and the oil may increase the viscosity of the sealantcomposition, thus aiding in the formation of a solidified mass withimproved dimensional stability under imposed stresses. Additionally, theabsorption of oil from an oil-based drilling fluid containing aninternal aqueous brine phase may lead to destabilization of the drillingfluid resulting in release of aqueous brine which will coagulate thelatex to form a resilient rubbery sealant mass. The amount oforganophilic clay present in the sealant composition may be in a rangeof from about 0.5% to about 50% by weight of the composition,alternately from about 5% to about 35% by weight of total composition,and alternately from about 10% to about 30% by weight of totalcomposition. When an organic solvent is used as a suspending solvent forthe solid latex, organophilic clay also may serve as a supending aid toprevent settling of the solid latex particles. Without limitation, asuitable organophilic clay is an alkyl quaternary ammonium bentoniteclay sold as CLAYTONE II by Southern Clay Products.

To improve the suspending ability of the sealant composition,particularly when they are aqueous fluids, viscosifying agents suitablefor increasing the viscosity of the sealant composition may be employed.Examples of such viscosifying agents include without limitationhydroxylethylcellulose, hydroxypropylcellulose, guar gum, hydroxyethyl-or hydroxypropyl-guar gum, etc. In an embodiment, a viscosifying agentis present in the sealant composition in an amount of from about 0.01%to about 1% by weight of the total composition.

In an embodiment the sealant composition comprises cross-linking agentsthat cross-link the latex and form a less deformable resilient rubberycomposition. Such cross-linking agents, along with cross-linkingaccelerators and retarders, are known to those skilled in the art. Inother embodiments, the solid latex may contain crosslinking agents thatare suitable for facilitating the formation of a resilient rubbery mass,which may be used during the polymerization stage of the monomers oradded to the latex prior to use (for example to the sealantcomposition). In embodiments wherein the solid latex containsvulcanizable groups such as the diene type of monomers, crosslinkingagents including vulcanizing agents such as sulfur,2,2′-dithiobisbenzothiazole, organic peroxides, azo compounds,alkylthiuram disulfides, selenium phenolic derivatives and the like;vulcanization accelerators such as fatty acids (e.g, stearic acid),metallic oxides (e.g., zinc oxide), aldehyde amine compounds, guanidinecompounds, disulfide thiuram compounds, and the like; vulcanizationretarders such as salicylic acid, sodium acetate, phthalic anhydride andN-cyclohexyl thiophthalimide; defoamers; or combinations thereof may beadded just prior to use, for instance to a sealant composition. Suchcompositions are discussed in U.S. Pat. No. 5,293,938, which isincorporated by reference herein in its entirety. If the crosslinkingagent is used during production of the latex, it may be amultifunctional monomer with more than one polymerizable group forexample divinylbenzene, trimethylolpropane triacrylate,tetraethyleneglycol diacrylate, methylene bisacrylamide, and the like.The type and amounts of the cross-linking agents will depend on thetemperature, and the rate at which the cross-linking will take place.Methods for determination of the amount of cross-linking agent based onthe reaction conditions are known to one of ordinary skill in the art.

In some embodiments, additives may be included in the sealantcomposition for improving or changing the properties thereof. Examplesof such additives include but are not limited to salts, accelerants, setretarders, defoamers, settling prevention agents, weighting materials,dispersants, vitrified shale, formation conditioning agents, orcombinations thereof. Other mechanical property modifying additives, forexample, carbon fibers, glass fibers, metal fibers, minerals fibers, andthe like can be added to further modify the mechanical properties or toaid further in preventing fluid losses.

Surfactants may be added to foam the cement slurry, to stabilize afoamed cement slurry, to stabilize a cement slurry containing a solidlatex against premature gellation or combinations thereof. Suchsurfactants may be anionic, alternatively noionic, and alternativelyzwitterionic. Examples of surfactants that stabilize latex emulsions incement slurries against premature gelling include without limitationSTABILIZER 434B latex stabilizer and STABILIZER 434C latex stabilizerneutral which are nonionic surfactants both available from HalliburtonEnergy Services. Examples of other surfactants suitable for use in thisdisclosure include without limitation ZONESEAL 2000 chemical additiveused in foam cementing applications and ZONESEAL 3000 chemical additiveused in foam cementing applications which are both foaming and foamstabilizing surfactants commercially available from Halliburton EnergyServices.

Any of the additives disclosed herein or known to one of ordinary skillin the art may be included singularly or in combination. Methods forintroducing these additives and their effective amounts are known to oneof ordinary skill in the art.

In an embodiment, the sealant composition comprising a solid latex iscontacted with a drilling mud. During drilling, a continuous flow ofdrilling ‘mud’ is circulated in the well. This mud is actually a thickmix of clay and other chemical additives in water or mineral oil, aswell as weighting agents such as barite (barium sulphate) to add weight.Drilling mud lubricates the bit, contains formation pressures, keeps thehole from collapsing and flushes rock chips and drill cuttings to thesurface. Two basic types of drilling fluids, or muds, are used in oilexploration and production: water-based (WBM) and oil-based muds (OBM).In an embodiment, the sealant composition comprising a solid latex maybe mixed with a OBM in a ratio varying from 10% to 90% by volume.Alternatively, the sealant composition comprising a solid latex may bemixed with a WBM in a ratio varying from 10% to 90% by volume.

In an embodiment, a pH-increasing additive (for example alkali, alkalineearth and transition metal metal hydroxides, carbonates, bicarbonates,phosphates, organic amines and the like) is added to the mud prior tocontacting with the fluid containing the solid latex, for example analkali swellable solid latex. For example, the pH of the mud (e.g., aWBM) may be adjusted to from about 10 to about 13 before contacting withthe fluid containing solid latex, for example an alkali swellable solidlatex. In an embodiment, the sealant composition may be mixed witheither a WBM or an OBM in the vicinity of loss circulation zone in atwo-stream method.

The addition of a solid latex or reconstituted solid latex to a sealantcomposition comprising a cement may improve the mechanical properties ofthe cement composition. Examples of improved mechanical propertiesinclude without limitation increased tensile strength, increasedcompressive strength, reduced elastic modulus and reduced brittleness.The addition of a solid latex to a cement composition may improve thetensile strength when compared to a similar formulation containing aliquid latex by from about 5% to about 50%, alternatively from about 10%to about 50%.

Sealant compositions comprising a solid latex and a cement may alsoproduce cement formations that are able to withstand the stressesassociated with cyclic loading encountered during the life of the well.In an embodiment, sealant compositions comprising a solid latex may havean increased latex content compared to sealant compositions comprisinglatex emulsions. Sealant compositions comprising a high latex contentmay display a reduced gas migration during cement settling and reducedfluid loss when compared to similar compositions having a lower latexcontent.

The sealant compositions comprising a solid latex may be introduced tothe wellbore to prevent the loss of aqueous or non-aqueous drillingfluids into loss-circulation zones such as voids, vugular zones, andnatural or induced fractures while drilling. In an embodiment, thesealant composition comprising a solid latex is placed into a wellboreas a single stream and activated by downhole conditions to form abarrier that substantially seals loss circulation zones. In such anembodiment, the sealant composition may be cementless. Such compositionsmay further comprise a pH-increasing additive in encapsulated orunencapsulated form. In an embodiment, the sealant compositioncomprising a solid latex and a mud (e.g., WBM or OBM) may function as afracture sealant slurry that may be used for drill ahead applications.

In yet another embodiment, a sealant composition may be formed downholeby the mixing of a first stream comprising a solid latex and a secondstream comprising a cement slurry, a pH increasing material, or both.The streams may be introduced in any order desired by the user. Methodsfor introducing compositions into a wellbore to seal subterranean zonesare described in U.S. Pat. Nos. 5,913,364; 6,167,967; and 6,258,757which are incorporated by reference herein in their entirety and U.S.Pat. No. 6,926,081B2 which was previously disclosed.

The sealant composition comprising a solid latex may form a non-flowing,intact mass inside the loss-circulation zone which plugs the zone andinhibits loss of subsequently pumped drilling fluid, which allows forfurther drilling. In an embodiment, the sealant composition solidifiesforming a mass which plugs the loss circulation zone at roomtemperature. Alternatively, the sealant composition solidifies forming amass, which plugs the loss circulation zone at temperatures of fromabout 45° F. to about 400° F.

It is to be understood that, it may be desired to hasten theviscosification reaction for swift plugging of the voids. Alternatively,it may be desired to prolong or delay the viscosification for deeperpenetration into the voids. For example the sealant may form a mass thatplugs the zone at elevated temperatures, such as those found at higherdepths within a wellbore.

In an embodiment, the sealant compositions may be employed in wellcompletion operations such as primary and secondary cementingoperations. Primary and secondary cementing operations refers towellbore completion processes as known to those skilled in the art, andsealant compositions for use in such cementing operations may or may notcontain cement. The sealant composition may be placed into an annulus ofthe wellbore and allowed to set such that it isolates the subterraneanformation from a different portion of the wellbore. The sealantcomposition comprising a solid latex thus forms a barrier that preventsfluids in that subterranean formation from migrating into othersubterranean formations. Within the annulus, the sealant compositionalso serves to support a conduit, e.g., casing, in the wellbore. In anembodiment, the wellbore in which the sealant composition is positionedbelongs to a multilateral wellbore configuration. It is to be understoodthat a multilateral wellbore configuration includes at least twoprincipal wellbores connected by one or more ancillary wellbores. Whensuch compositions contain cement, the resulting sealant has improvedmechanical properties to resist cyclic pressure and pressure inducedstresses imposed during the well operations. When such sealantcompositions do not contain cement, the sealant mass is resilient andmay be characterized by a low elastic modulus and being well suited tosustain cyclic stresses during the well bore operations.

In secondary cementing, often referred to as squeeze cementing, thesealant composition may be strategically positioned in the wellbore toplug a void or crack in the conduit, to plug a void or crack in thehardened sealant (e.g., cement sheath) residing in the annulus, to pluga relatively small opening known as a microannulus between the hardenedsealant and the conduit, and so forth. Various procedures that may befollowed to use a sealant composition in a wellbore are described inU.S. Pat. Nos. 5,346,012 and 5,588,488, which are incorporated byreference herein in their entirety.

In an embodiment, the sealant composition comprising solid latex but nocementitious material may be used in well completion operations such asprimary operations (e.g., primary cementing). As an example, they may beplaced behind expandable casings or used for consolidating gravel packsor incompetent formations. Further, such sealant compositions may beused in remedial operations such as secondary cementing, sealing leaks,cracks, or voids and forming temporary plugs for the purpose ofisolating zones to divert subsequent fluids and the like.

Additional disclosure regarding the use of cementless sealantcompositions for such applications can be found in U.S. Pat. Nos.5,159,980 and 6,668,928, which are incorporated by reference herein intheir entirety.

In other embodiments, additives are also pumped into the wellbore withthe sealant composition. For instance, fluid absorbing materials,particulate materials, resins, aqueous superabsorbers, viscosifyingagents, suspending agents, dispersing agents, or combinations thereofcan be pumped in the stream with the sealant compositions disclosed.

EXAMPLES

The invention having been generally described, the following examplesare given as particular embodiments of the invention and to demonstratethe practice and advantages thereof. It is understood that the examplesare given by way of illustration and are not intended to limit thespecification of the claims in any manner.

Example 1

A sealant composition containing a solid latex and no cementitiousmaterial was prepared and the mechanical properties of the compositiondetermined. A reconstituted solid latex emulsion was prepared by (a)blending a styrene-butadiene latex powder (33 grams) supplied by RhodiaCorporation as 04-OF-006 with a solid blend (40 grams) FLEXPLUG OBM lostcirculation material which contains an organophilic clay; a viscosifyingpolymer xanthan gum; a particle dispersing sulfonatednaphthalene-formaldehyde condensate; and sodium carbonate and iscommercially available from Halliburton Energy Services (b) mixing thedry blend with water (95 ml) containing the liquid stabilizer surfactant(7.5 ml) sold as STABILIZER 434C latex stabilizer and D-AIR 3000Lantifoaming agent which is a defoamer both available from HalliburtonEnergy Services. The mixture was stirred until the viscosity andrheology of the emulsion stabilized.

Sealant composition sample A was formed by mixing the stabilizedemulsion with an equal volume of OBM drilling fluid sold as INVERMUL RFby Baroid Drilling Fluids, and the resulting product did not form aviscous mass and had a yield point (YP) of 0 Pa. Sealant compositionsample B, a comparative sample, was formed by mixing INVERMUL RFemulsifier which is a drilling fluid and a sealant composition formed byreplacing the solid latex in the sealant composition Sample A with LATEX2000 cement additive which is an aqueous latex emulsion commerciallyavailable from Halliburton Energy Services and reducing the water amountto 66 ml as described above. A viscous mass having a yield point of 2700Pa was formed at room temperature in less than 10 minutes from sealantcomposition Sample B. Samples A and B were heated in a water bath at180° F., and upon heating, the YP of both compositions increased.Specifically, Sample B having containing the aqueous latex had a YPincrease from 2700 to 4100 Pa while Sample A having the solid latex hada YP increase from 0 to 2700 Pa.

The results demonstrate the ability of an OBM and solid latexcomposition to form a viscous mass. The retention of fluidity until thesealant composition was heated is an advantageous feature allowing fordeeper penetration of the treatment into the fracture beforesolidification. This may improve the ability of the viscous mass towithstand the drilling fluid's hydrostatic pressure thus allowing forcontinued drilling at the same or increased mud density.

Example 2

A sealant composition similar to Sample A containing a solid latex andno cementitious material was prepared and the mechanical properties ofthe composition determined as described in EXAMPLE 1. However, thecomposition did not contain the liquid stabilizer surfactant STABILIZER434C latex stabilizer. The final results were similar to those describedin Example 1 in which the stabilizing surfactant was used. Theseobservations suggest that stabile emulsions can be obtained withoutusing the surfactants.

Example 3

The ability of the sealant compositions containing a solid latex toprevent water-based mud (WBM) losses was examined. A solid latexsuspension was formed by (a) blending styrene-butadiene latex powder (48grams) with a solid blend (220 grams) containing an organophilic clayCLAYTONE II organophilic bentonite which is an organoclay commerciallyavailable from Southern Clay Products, a viscosifying polymer xanthangum, and bentonite and (b) mixing the dry blend with a nonaqueous fluidsuch as diesel (350 ml). The slurry was then mixed with a WBM (350 ml).The resulting mixture formed a viscous mass with a yield point similarto a system that did not contain the dry latex however the surface ofthe viscous mass had a slick sheen created by the latex. The resultsdemonstrate the ability of the sealant composition containing a solidlatex to form a viscous mass when contacted with a WBM. Furthermore, thesurface coating on the viscous mass could reduce the plastic viscosityof the mass allowing for a reduction in the required horsepower neededto the place the final product.

Example 4

A 16.4 pounds per gallon cement slurry was prepared with Class H cement,water (as specified in Table 1) and either solid latex or an aqueouslatex emulsion according to American Petroleum Institute (API)Recommended Practice 10B, 22^(nd) Edition 1997 with the exception thatwhen aqueous latex emulsion was used the blender stirring rate was keptat 1000 rpm. The latex slurry was prepared by adding, D-AIR 3000Lantifoaming agent which is a defoamer and, STABILIZER 434C latexstabilizer (10% by volume of the latex) which is a nonionic surfactantboth of which are available from Halliburton Energy Services to thelatex in the mix water followed by addition of cement with agitation at1000 rpm for 45 seconds. A control slurry comprising Class H cement andwater was prepared according to the API Specification mentioned inTable 1. The mechanical property modification of cement compositions bythe solid and aqueous latexes was measured by comparing the mechanicalproperties of the latex cement compositions to the control slurry. Theslurries were poured into tensile dog-bone shaped briquettes accordingto the procedure described for the test CRD-C260-01 in the U.S. ArmyCorps of Engineers' Handbook for Concrete and Cement. The slurry wasalso poured into 2″×5″ cylindrical brass molds to perform load versusdisplacement studies under unconfined conditions using MTS load frameequipment manufactured by MTS Systems Corporation of Eden Prairies,Minnesota according to ASTM D3148-02 (Standard Test Method for ElasticModuli of Intact Rock Core in Uniaxial Compression). The cylindricalsamples and the tensile briquettes were cured in autoclave at 190° F.under a pressure of 3000 psi for 72 hrs. The tensile strengths weremeasured on a Tinius Olsen Strength Tester equipment. The results arepresented in Table 1. TABLE 1 Amount of Solid Young's Water % aqueouslatex, Latex Slurry Compressive Tensile Mosulus × by wt. of Aqueousgal/sk (% active Solid Latex amount, Density, Strength³, Strength, 10⁶,Poisson's cement latex type content bwoc) type bwoc ppg psi psi psiratio 39.42 None None 16.4 8230 430 2.34 0.207 33.2 Styrene- 0.7 (3.1%)16.3 4480 470 1.32 0.199 butadiene 36.81 Styrene 2% 16.4 8800 700 2.190.183 Butadiene¹ 35.15 Same 4% 16.4 9390 680 2.25 0.204 36.16 Styrene 4%16.4 7650 700 1.82 0.200 Butadiene²¹From Rhodia Corporation²From Dow Reichhold Corporation³From load displacement measurements under unconfined conditions

The results in Table 1 suggest that solid latexes provide substantiallydifferent mechanical properties than the aqueous latex fluids when addedto cement. The results demonstrate that the addition of dry latexmaterial to the above described cement compositions produce cementcompositions with increased tensile strengths, compressive strengths andelastic moduli when compared to similar compositions prepared usingaqueous latex emulsions.

Without intending to be limited by theory, this behavior may be areflection of the timing difference between settling of cement and thetime it takes for the dry latex to achieve the same structural form asthat in the original aqueous latex. One consequence of this timingdifference is the different degrees of film forming of a latex whenadded to a cement slurry in the aqueous or dry form.

While preferred embodiments of the invention have been shown anddescribed, modifications thereof can be made by one skilled in the artwithout departing from the spirit and teachings of the invention. Theembodiments described herein are exemplary only, and are not intended tobe limiting. Many variations and modifications of the inventiondisclosed herein are possible and are within the scope of the invention.Where numerical ranges or limitations are expressly stated, such expressranges or limitations should be understood to include iterative rangesor limitations of like magnitude falling within the expressly statedranges or limitations (e.g., from about 1 to about 10 includes, 2, 3, 4,etc.; greater than 0.10 includes 0.11, 0.12, 0.13, etc.). Use of theterm “optionally” with respect to any element of a claim is intended tomean that the subject element is required, or alternatively, is notrequired. Both alternatives are intended to be within the scope of theclaim. Use of broader terms such as comprises, includes, having, etc.should be understood to provide support for narrower terms such asconsisting of, consisting essentially of, comprised substantially of,etc.

Accordingly, the scope of protection is not limited by the descriptionset out above but is only limited by the claims which follow, that scopeincluding all equivalents of the subject matter of the claims. Each andevery claim is incorporated into the specification as an embodiment ofthe present invention. Thus, the claims are a further description andare an addition to the preferred embodiments of the present invention.The discussion of a reference herein is not an admission that it isprior art to the present invention, especially any reference that mayhave a publication date after the priority date of this application. Thedisclosures of all patents, patent applications, and publications citedherein are hereby incorporated by reference, to the extent that theyprovide exemplary, procedural or other details supplementary to thoseset forth herein.

1. A method of servicing a wellbore comprising placing a sealantcomposition comprising solid latex into the wellbore.
 2. The method ofclaim 1 wherein the solid latex is prepared by removing water from anaqueous latex solution.
 3. The method of claim 2 wherein the emulsionpolymerized latex system comprises vinyl aromatic monomers, ethylene,butadiene, vinylnitrile, olefinically unsaturated esters of C₁-C₈alcohol, ethylenically unsaturated carboxylic acids or combinationsthereof
 4. The method of claim 2 wherein the emulsion polymerized latexsystem comprises a colloidally stabilized latex, an alkali swellablelatex or combinations thereof.
 5. The method of claim 1 wherein thesolid latex is reconstituted by mixing the dry latex with an aqueoussolution, a non-aqueous solution or combinations thereof.
 6. The methodof claim 1 wherein the sealant composition further comprises an anionicsurfactant, a nonionic surfactant, a zwitterionic surfactant orcombinations thereof.
 7. The method of claim 1 wherein the sealantcomposition further comprises cement.
 8. The method of claim 1 whereinthe solid latex is an alkali swellable solid latex or derivative thereofand the sealant composition further comprises a pH-increasing material.9. The method of claim 8 wherein the pH-increasing material is an alkalimetal hydroxide, alkaline earth metal hydroxide, transition metalhydroxide, carbonate, bicarbonate, phosphate, organic amine, orcombinations thereof.
 10. The method of claim 1 wherein the sealantcomposition further comprises an organophilic clay.
 11. The method ofclaim 1 wherein the sealant composition further comprises a viscosifier.12. The method of claim 1 further comprising contacting the sealantcomposition with a drilling mud.
 13. The method of claim 12 wherein themud comprises a pH-increasing material and solid latex is an alkaliswellable solid latex.
 14. The method of claim 1 wherein the sealantcomposition further comprises a cross-linking agent, a vulcanizationaccelerator, a vulcanization retarder, or combinations thereof.
 15. Themethod of claim 14 wherein the cross-linking agent comprises sulfur,2,2′-dithiobisbenzothiazole, organic peroxides, azo compounds,alkylthiuram disulfides, selenium phenolic derivatives, or combinationsthereof.
 16. The method of claim 14 wherein the vulcanizationaccelerators comprises a fatty acid, metallic oxides), aldehyde aminecompound, guanidine compounds, disulfide thiuram compounds, orcombinations thereof.
 17. The method of claim 14 wherein thevulcanization retarder comprises salicylic acid, sodium acetate,phthalic anhydride, N-cyclohexyl thiophthalimide, defoamers, orcombinations thereof.
 18. The method of claim 1 wherein servicing thewellbore comprises completing the wellbore.
 19. The method of claim 1wherein servicing the wellbore comprises primary or secondary cement ofthe wellbore.
 20. The method of claim 1 wherein servicing the wellborecomprises reestablishing circulation following a loss of circulation inthe wellbore.
 21. The method of claim 20 further comprising drillingahead upon reestablishing circulation in the wellbore.
 22. The method ofclaim 1 wherein servicing the wellbore comprises sealing a permeablezone in the wellbore.